Reland of mac and ios: Build third-party code with -Wall.

build/common.gypi

 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # IMPORTANT:
 # Please don't directly include this file if you are building via gyp_chromium,
 # since gyp_chromium is automatically forcing its inclusion.
 {
   # Variables expected to be overriden on the GYP command line (-D) or by
   # ~/.gyp/include.gypi.
@@ skipping 3192 matching lines @@
               # TODO(darin): Unfortunately, some third_party code depends on base.
                 'msvs_disabled_warnings': [
                   4251,  # class 'std::xx' needs to have dll-interface.
                  ],
               }],
             ],
           }],
 
           [ 'OS=="mac" or OS=="ios"', {
             'xcode_settings': {
-              'WARNING_CFLAGS!': ['-Wall', '-Wextra'],
+              'WARNING_CFLAGS!': ['-Wextra'],
             },
             'conditions': [
               ['buildtype=="Official"', {
                 'xcode_settings': {
                   'GCC_TREAT_WARNINGS_AS_ERRORS': 'NO',    # -Werror
                 },
               }],
             ],
           }],
           [ 'OS=="ios"', {
@@ skipping 3200 matching lines @@
     # settings in target dicts.  SYMROOT is a special case, because many other
     # Xcode variables depend on it, including variables such as
     # PROJECT_DERIVED_FILE_DIR.  When a source group corresponding to something
     # like PROJECT_DERIVED_FILE_DIR is added to a project, in order for the
     # files to appear (when present) in the UI as actual files and not red
     # red "missing file" proxies, the correct path to PROJECT_DERIVED_FILE_DIR,
     # and therefore SYMROOT, needs to be set at the project level.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }